Pineal modulation of reproduction is well documented. Although the indoleamine melatonin is established as a, or the , pineal antigonadotropin, a large body of evidence suggests that non-indolic, ostensibly polypeptidic, antigonadotropic substances are present in mammalian pineal gland extracts as well. The goal of this project is to determine the chemical structure and physiological mechanisms of action of pineal peptides involved in the regulation of reproduction. A primary candidate is the non-mammalian neurohypophysial hormone vasotocin (AVT). Methods are established for the purification of a pineal antigonadotropin (PAG) from dilute acetic acid extracts of bovine pineal glands. The antigonadotropic substance is inactivated by proteolytic enzymes. When injected into mica and rats this potential hormone retards puberty inhibits fertility and blocks ovulation. It may act at hypothalamic levels, through effects on the synthesis of catecholamines. During the first two years of this project more than ten kg of bovine pineals were fractionated, providing peptides of interest in sufficient quantities for structure determination by automated sequential analysis. Arginine vasopressin and oxytocin were isolated by sequential semipreparative high performance liquid chromatography, and their primary structures determined, whereas the putative pineal antigonadotropin AVT was not identified. Several peptides of unknown structure were isolated which demonstrate antigonadotropic, neurohypophysial hormone-like or LHRH- like activity. These substances have been obtained in quantities sufficient for initial primary structure determinations during the next year. Studies will continue also on a novel, threonine-rich decapeptide isolated during the last year, with the goal of determining its relationship to the PAG under investigation. As structures of peptides affecting reproduction become known, synthesis of analogs will be accomplished in order that detailed physiological studies of their mechanisms of actions can be carried out.